Method and apparatus for producing unconventional oil at shallow depths

ABSTRACT

An oil production well is drilled into a kerogenous chalk source rock comprising (i) type IIs kerogen and (ii) shallow naturally-occurring unconventional oil derived from the type IIs kerogen that is resident within pore space of the source rock. In some embodiments, the production well is drilled at a location where the geothermal gradient is at least 3 degrees C. per 100 m is present at or near the production well. It is believed that the presence of this geothermal gradient accelerated maturation of the type IIs kerogen of the source rock to convert a portion of the type IIs kerogen into the unconventional oil. In some embodiments, the shallow production well is non-vertical. In some embodiments, at depths that are shallow and within the source rock, the production well is cased and perforated. Oil from the source rock may be produced via the production well and the shallow-depth perforated locations thereof.

BACKGROUND AND RELATED ART

In the last few years, the oil industry in the United States hasdeveloped methods for producing unconventional gas and oil from very lowpermeability source rocks. In these unconventional gas and oil plays,the gas and oil is still contained within the original source rock andhas not migrated to a reservoir and trap.

For example, the Bakken shale in North Dakota has been extensivelyproduced using long horizontal wells which are stimulated with multiplepropped hydraulic fractures. These Bakken wells are typically at depthsgreater than about 3000 m in order for the Type I kerogen to havematured over geological time sufficiently to generate oil and gas. Eventhough the Bakken oil produced is low viscosity and rich in NGL (naturalgas liquids), because of the depth of the wells and the many stages ofhydraulic stimulation that are required, these unconventional wells arevery expensive and only a very small percentage of the unconventionaloil and gas in place is actually produced.

SUMMARY OF EMBODIMENTS

Instead of relying on artificial heat to pyrolyze kerogen of akerogenous chalk into pyrolysis fluids (i.e. as is common in in-situconversion processes (ICP)), it is possible to drill for oil in akerogenous chalk where natural events (e.g. historical volcanic or othergeothermal activities) supplied sufficient thermal energy to convertkerogen of the source rock into naturally-occurring oil. In particular,the present invention relates to techniques where production wells (e.g.shallow wells) are drilled into a kerogenous chalk that is characterizedby Type IIs kerogen, a porosity of at least 30% and at a location wherethe geothermal gradient is at least 3 degrees Celsius per 100 meters.

In contrast with the aforementioned ICP techniques where (i) oil is onlycreated within the subsurface after an extended period of time (e.g. atleast months or years) and where (ii) there is a need to investsignificant thermal energy in order to pyrolyze kerogen, according tothe presently-disclosed techniques, it is possible to producenaturally-occurring oil with little or no subsurface heating required.

One salient feature of the present invention is that the production wellis shallow—i.e. having a maximum depth of at most 2 kilometers. This isin contrast to conventional techniques where significantly deeperproduction wells are required to access naturally occurring oil.Advantageously, the shallow production wells of the present inventioncan be provided at a mush lower cost than would be required for deeperproduction wells.

Surprisingly, it is now disclosed for the first time that it is possibleto find naturally-occurring oil at these relatively shallow depths incoastal/marine formations and/or in locations where there was nosignificant uplift to the source rock or sediment and/or in locationslacking significant non-conformities.

Furthermore, by selecting kerogenous chalk having a porosity of at least30%, it is possible to access locations where a greater quantity ofnaturally-occurring oil is located in pore space of the source rock.

In some embodiments, the geothermal gradient is at least 3.5 degreesCelsius per 100 meters or at least 4 Celsius per 100 meters.

It is now disclosed a method of unconventional oil productioncomprising:

-   -   a. drilling a production well into a kerogenous chalk source        rock comprising (i) type IIs kerogen and (ii) shallow        naturally-occurring unconventional oil derived from the type IIs        kerogen that is resident within pore space of the source rock;    -   b. at shallow depths of at most 2 kilometers and within the        source rock, casing and perforating the production well; and    -   c. producing the shallow naturally-occurring unconventional oil        from the source rock via the production well.

In some embodiments, a location at which the production well is drilledis selected in accordance with a geothermal gradient.

In some embodiments, the production well is drilled at a location wherethe geothermal gradient is at least 3.0 degrees Celsius per 100 meters,or at least 3.5 degrees Celsius per 100 meters, or at least 4.0 degreesCelsius per 100 meters.

In some embodiments, the unconventional oil and at least some of theperforations of the production well are located at depths of at most 1.5kilometers, or at most 1200 meters, or at most 1 kilometer or at most800 meters.

In some embodiments, the source rock is below an overburden comprising abasalt layer.

In some embodiments, the overburden further comprises a sedimentaryportion situated below the basalt layer so that horizontal stresses ofthe sedimentary portion were locked in at or before a time of depositionof the lava flow which formed the basalt layer.

In some embodiments, a porosity of the source rock is at least 30% or atleast 35% or at least 40%.

In some embodiments, a permeability of the source rock matrix is at most1 mD or at most 0.1 mD or at most 0.01 mD.

In some embodiments, an oil saturation of pore space of the source rockis at least 50% or at least 60% or at least 70%.

In some embodiments, the source rock is stimulated at the shallow depthsto increase a permeability of the source rock.

In some embodiments the stimulation of the source rock occurs at a depththat is less than that of all aquifers thereof.

In some embodiments the source rock is stimulated by means other than byhydraulic stimulation.

In some embodiments, a total organic content (TOC) of the source rock isat least 10%.

In some embodiments, the source rock is stimulated at the shallow depthsby high pressure acid stimulation of the source rock.

In some embodiments, the source rock is hydraulic stimulated.

In some embodiments, the source rock thermally stimulated.

In some embodiments thermal energy is effective to significantlyincrease the mobility of the naturally-occurring oil by at least afactor of 10.

In some embodiments thermal energy is effective to significantlydecrease the viscosity of the naturally-occurring oil by at least afactor of 10.

In some embodiments the thermal energy is effective to vaporize liquidwater and light hydrocarbons within the pore space of the source rock.

In some embodiments, pressurized steam is injected into the source rockat the shallow depths so as to thermally stimulate the source rock toincrease a mobility of the unconventional oil.

In some embodiments the steam is injected according to a huff-and-pufftechnique.

In some embodiments the steam enters the source rock at a temperature ofat most 200 degrees Celsius.

In some embodiments, the production well is non-vertical.

In some embodiments the non-vertical production well is substantiallyhorizontally-oriented.

In some embodiments the stimulation forms a plurality of parallel, thinflow channels within the source rock that are each substantiallyvertically oriented, a thickness direction of the flow channels beingalong a central axis of the production well, and with each flow channelleading to the production well.

In some embodiments, the production well is substantially horizontal, acentral axis thereof being substantially parallel to a minimum stressvector of the kerogenous chalk source rock.

In some embodiments, a total organic content (TOC) of the source rock isat least 15%.

In some embodiments, a sulfur content of the unconventional oil is atleast 2.5% wt/wt or at least 3% wt/wt or at least 3.5% wt/wt or at least4% wt/wt.

In some embodiments, an API gravity of the unconventional oil is atleast 20° and/or at most 30°.

In some embodiments, a maximum depth of the production well is at most 2km or at most 1.5 kilometers, or at most 1200 meters, or at most 1kilometer or at most 800 meters.

In some embodiments, oil produced via the production wells is neverheated within the source rock to a temperature exceeding 200 degreesCelsius In some embodiments carried out so that bulk source rock isnever heated to a temperature exceeding 200 degrees Celsius.

In some embodiments, the method is carried out without significantlypyrolyzing the source rock.

In some embodiments, a majority of hydrocarbon liquids produced via theproduction wells is the naturally-occurring oil.

In some embodiments the producing includes drawing naturally-occurringoil residing in pore space of the kerogenous chalk source rock into theproduction well.

In some embodiments the producing includes drawing naturally occurringoil residing in the pore space of the kerogenous chalk source rock intothe production well via perforations thereof.

In some embodiments comprising subjecting the produced oil to adistillation process.

It is now disclosed an apparatus for unconventional oil productioncomprising:

-   -   a production well drilled into a kerogenous chalk source rock        comprising (i) type IIs kerogen and (ii) shallow        naturally-occurring unconventional oil derived from the type IIs        kerogen that is resident within pore space of the source rock,    -   wherein the production well is cased and perforated at shallow        depths of at most 2 kilometers and within the source rock so        that the shallow naturally-occurring unconventional oil is        recovered by the production well via the shallow-depth        perforations of the production well.

In some embodiments the production well is non-vertical.

In some embodiments the production well is horizontal.

In some embodiments further comprising a series of thin parallel flowchannels that are all vertically oriented and transverse to a centralaxis of the production well.

In some embodiments wherein the production well is substantiallyhorizontal, a central axis thereof being substantially parallel to aminimum stress vector of the kerogenous chalk.

In some embodiments wherein at a location of the production well, alocal geothermal gradient is at least 3.0 degrees Celsius per 100meters, or at least 3.5 degrees Celsius per 100 meters, or at least 4.0degrees Celsius per 100 meters.

In some embodiments the unconventional oil and at least some of theperforations of the production well are located at depths of at most 1.5kilometers, or at most 1200 meters, or at most 1 kilometer or at most800 meters.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 3, 5, and 10 are flow charts of methods of producingnaturally-occurring oil that resides in pore space of a kerogenouschalk.

FIGS. 2, 4, and 6-9 illustrate subsurface production wells.

FIG. 11 illustrates a geothermal gradient from a well log.

DETAILED DESCRIPTION OF EMBODIMENTS

The invention is herein described, by way of example only, withreference to the accompanying drawings. With specific reference now tothe drawings in detail, it is stressed that the particulars shown are byway of example and for purposes of illustrative discussion of thepreferred embodiments of the exemplary system only and are presented inthe cause of providing what is believed to be a useful and readilyunderstood description of the principles and conceptual aspects of theinvention. In this regard, no attempt is made to show structural detailsof the invention in more detail than is necessary for a fundamentalunderstanding of the invention, the description taken with the drawingsmaking apparent to those skilled in the art how several forms of theinvention may be embodied in practice and how to make and use theembodiments.

For brevity, some explicit combinations of various features are notexplicitly illustrated in the figures and/or described. It is nowdisclosed that any combination of the method or device featuresdisclosed herein can be combined in any manner—including any combinationof features—any combination of features can be included in anyembodiment and/or omitted from any embodiments.

FIG. 1A-1C are flow charts of a method of producing naturally-occurringoil that resides in pore space of a kerogenous chalk optionally at alocation where there is a significant geothermal gradient. For thepresent disclosure, a ‘significant’ geothermal gradient is at least 3degrees Celsius/100 meters. In some embodiments, the geothermal gradientis at least 3.5 degrees Celsius/100 meters or at least 4.0 degreesCelsius/100 meters or about 4.5 degrees Celsius/100 meters.

The kerogenous chalk is characterized by Type IIs kerogen and may have aporosity of at least 30% (in some embodiments, at least 35% or at least40% or at least 45% or at least 50%). Because of the relatively largeporosity, a large amount of naturally-occurring oil may be storedtherein.

In step S101 a shallow production well (i.e. see 224 of any of FIG. 2,4, 6 or 8-10) is drilled into the kerogenous chalk source rock (i.e. see800 of FIG. 2, 4 or 6) that is characterized by type IIs kerogen andoptionally at a location where there is a geothermal gradient of atleast 3 degrees Celsius per 100 meters. For the present disclosure, adepth (e.g. a depth ‘within the source rock’) is measured relative tothe surface and not relative to the highest location in the source rock.For the present disclosure, the term ‘shallow’ refers to a maximum depthof at most 2 kilometers—in some embodiments, at most 1.5 kilometers, orat most 1200 meters, or at most 1 kilometer, or at most 800 meters, orat most 750 meters.

The production well of step S101 is ‘shallow’—i.e. has a maximum depththat is ‘shallow.’ In step S105, at depths that are (i) shallow, (ii)optionally above the aquifer and (iii) within the source rock 800, theproduction well is cased and perforated. The ‘shallow depth’ of thecasing and perforating may be less than the maximum depth of theproduction well which is also ‘shallow.’ For example, the well may becased or perforated at a maximum depth of about 1.5 kilometers, or atmost 1200 meters, or at most 1 kilometer or at most 800 meters.

In step S109, naturally-occurring oil from the source rock may beproduced via the shallow-depth perforations of the production well. Forexample, the producing may include drawing naturally occurring oilresiding in pore space of the kerogenous chalk source rock into theproduction well. As noted above, the high porosity means that largerquantities of naturally-occurring oil may be stored than would bepossible if the porosity of the source rock was lower.

In the examples of FIGS. 1B, 3B, 5B and 10B, the drilling of theproduction well is continent upon geothermal conditions beingsatisfied—e.g. a minimal temperature gradient.

In the examples of FIGS. 1C, 3C, 5C and 10C, the drilling of theproduction well is contingent upon a basalt overburden condition beingsatisfied—e.g. a minimum thickness or a greater thickness than that inneighboring locations.

In one non-limiting example, magnetotelluric techniques may be employedto measure a thickness of the basalt overburden.

FIG. 2 illustrates an apparatus related to the method of FIG. 1.Illustrated in FIG. 2 are the overburden 820 (e.g. a basalt overburden),the kerogenous chalk 800, the aquifer 830, a production well 224.

In the example of FIG. 2B, a stimulated zone 870 is formed within thekerogenous chalk source rock 800. In the example of FIG. 2C, multiplestimulated zones 870 at different depths are formed within thekerogenous chalk source rock 800.

FIG. 3 is a flow chart of a method where the production well isnon-vertical—e.g. horizontal. Although well perforations 860 at shallowdepths are not illustrated in any of FIGS. 4, 6, 8-10, it is appreciatedthat the well perforations 860 may be provided in any embodiment, andnot just that of FIG. 2. FIG. 4 illustrates an apparatus related to themethod of FIG. 3.

As illustrated in FIG. 5, optionally, it is possible to stimulate thesource rock at the shallow depths (e.g. above all aquifers) so as tomobilize naturally-occurring oil within the kerogenous chalk source rock800. In some embodiments, this creates a series of parallel flowconduits towards the production well 224 through which thenaturally-occurring oil may flow. In this sense, the stimulation of thekerogenous chalk source rock 800 may increase the ability of thenaturally-occurring oil to flow to production well 224, and thus may besaid to ‘mobilize’ the naturally-occurring oil.

FIGS. 6 and 9 illustrate a series of thin flow channels, for example,shaped like discs. Each flow channel leads to production well 224 and isvertically oriented. Each flow channel is a transverse fracture.

In contrast, in the example of FIGS. 7-8, longitudinal fractures areillustrated. It is noted that transverse fractures are significantlymore efficient for transporting oil within the chalk formation to theproduction well—thus, the transverse fractures of FIGS. 6 and 9 arepreferred to the longitudinal fractures of FIGS. 7-8.

In all of FIGS. 7-9, the production well 224 is horizontal so that acentral axis thereof is in the horizontal plane. In the example of FIG.7, the minimum stress direction is vertically-oriented—i.e in the zdirection. In the example of FIG. 8-9, the minimum stress direction ishorizontally-oriented—however, in the example of FIG. 9, the centralaxis of the production well 224 is substantially co-linear with a stressaxis of the formation.

As noted earlier, in order to attain the geometry of FIGS. 6 and 9, itmay be preferred that the minimum stress axis is in the horizontalplane. Thus, it may be preferred to locate the horizontal productionwell where there is significant vertical stress. A presence of densebasalt in the overburden, and preferably an existence of a relativelythick basalt overburden, increases the vertical stress within theformation, and allows the deployment of horizontal production wellstogether with vertical transverse fractures at a depth less than whatwould be possible in the absence of the basalt.

Because of the relatively large density of basalt (i.e. over 70% greaterthan that of chalk), a presence of the basalt overburden increases avertical stress/pressure in the kerogenous chalk. During deposition ofthe sediments, the resulting horizontal stresses, contained within stifflateral boundaries, are locked in place. Basalt flows, resulting fromvolcanic eruptions, are added on top of the sedimentary deposits. Assuch, a ratio between the vertical stress and horizontal stresses isconcomitantly increased by the basalt accumulations, and for relativelyshallow depths (i.e. significantly shallower than would be observed inthe absence of the basalt overburden), the vector of minimum stress isin the horizontal plane. As will be discussed below, this is useful forsituations where it is desired to stimulate the kerogenous chalk sourcerock so as to form a series of vertical flow channels which each lead toproduction well 224 and which are transverse fractures relative centralaxis of the production well 224. The fracture direction in shallowformations may not necessarily be vertical. If during stimulation aconfined fracture leads to an additional net pressure, then thehydrofracture may start vertical and then turn horizontal. These complex“T”-shaped hydrofractures are usually bad for oil production because thewidth of the horizontal branch may be very small resulting in screenoutswhere the slurry fails to transport the proppant because the proppantcannot be transported beyond the point where the fracture width issmaller than three proppant diameters. The thin horizontal branches maylead to an excessive pressure increase that prevents further lateralfracture growth.

Thus, it is desirable to have a shallow location where the verticalstress is sufficiently greater than the horizontal stresses to assurethat the hydrofractures are vertical. Thus it is desirable to havesufficient overburden of high density basalt. Basalt has a high densityof about 3 gm/cc, and a basalt flow on top of the sedimentary cover addssignificant vertical stress. For example, 100 m of basalt on the surfaceadds over 400 psi of vertical stress, thus assuring that a hydrofracturewill be oriented vertically.

In the example of FIG. 9, a thickness direction 890 of each flow channelis along the central axis of the production well 224.

In the examples of FIG. 5-9 the source rock is stimulated to mobilizenaturally-occurring oil. This is not a requirement.

Alternatively or additionally, it is possible to introduce thermalenergy into the kerogenous source rock as to increase the mobility ofnaturally occurring oil therein—e.g. by reducing the viscosity thereofor by facilitating the removal of water or brine from the pore space ofthe kerogenous chalk so as to increase the relatively permeability ofthe naturally-occurring oil therein.

As noted above, in some embodiments, there is a geothermal gradient ofat least 3 degrees Celsius per 100 meter. FIG. 11 illustrates data froma well log where the geothermal gradient is about 4.4 degrees Celsiusper 100 meter.

Additional Discussion

Some embodiments of the present invention relate to a method of oilproduction comprising: a. drilling a shallow production well having amaximum depth of at most 2 kilometers into a kerogenous chalk sourcerock that is characterized by a. type IIs kerogen; at a location wherethere is a geothermal gradient of at least 3 degrees Celsius per 100meters; and b. at depths that are shallow, above the aquifer and withinthe source rock, casing and perforating the production well; c.producing naturally-occurring oil from the source rock via theproduction well and the shallow-depth perforated locations thereof.

Some embodiments of the present invention relate to a method of oilproduction comprising: a. drilling a shallow non-vertical productionwell having a maximum depth of at most 2 kilometers into a kerogenouschalk source rock that is characterized by: i. type IIs kerogen; and ii.a geothermal gradient of at least 4 degrees Celsius per 100 meters andc. producing naturally-occurring oil from the source rock via thenon-vertical production well.

In some embodiments, the non-vertical production well is substantiallyhorizontally-oriented.

Some embodiments of the present invention relate to a method of oilproduction comprising: a. drilling a shallow production well having amaximum depth of at most 2 kilometers into a kerogenous chalk sourcerock that is characterized by: i. type IIs kerogen; and ii. a geothermalgradient of at least 4 degrees Celsius per 100 meters and b. stimulatingthe source rock at the shallow depths so as to mobilizenaturally-occurring oil therein; and c. producing from the source rock,via the production well, the mobilized naturally-occurring oil.

In some embodiments, the production well is non-vertical.

In some embodiments, the non-vertical production well is substantiallyhorizontally-oriented.

In some embodiments, the stimulation forms a plurality of parallel, thinflow channels within the source rock that are each substantiallyvertically oriented, a thickness direction of the flow channels beingalong a central axis of the production well, and with each flow channelleading to the production well.

In some embodiments, the stimulation of the source rock occurs at adepth that is less than that all aquifers thereof.

Some embodiments of the present invention relate to a method of oilproduction comprising: a. drilling a shallow production well having amaximum depth of at most 2 kilometers into a kerogenous chalk sourcerock that is characterized by: i. type IIs kerogen; and ii. a geothermalgradient of at least 4 degrees Celsius per 100 meters and b. introducingthermal energy into the source rock so as to increase a mobility ofnaturally-occurring oil in the source rock; and c. producing, via theproduction wells, the increased-mobility naturally-occurring oil fromthe dried portions of the oil shale source rock.

In some embodiments, thermal energy is effective to significantlyincrease a mobility of the naturally-occurring oil by at least a factorof 10.

In some embodiments, the thermal energy is effective to significantlydecrease the viscosity of the naturally-occurring oil by at least afactor of 10.

In some embodiments, the thermal energy is effective to vaporize liquidwater within the pore space of the source rock so as to increase therelative permeability of the naturally-occurring oil within the sourcerock.

In some embodiments, oil produced via the production wells is neverheated within the source rock to a temperature exceeding 200 degreesCelsius.

In some embodiments, the method is carried out so that the bulk sourcerock is never heated to a temperature exceeding 200 degrees Celsius.

In some embodiments, the method is carried out without significantlypyrolyzing the source rock.

In some embodiments, a majority of hydrocarbon liquids produced via theproduction wells is naturally occurring.

In some embodiments, the geothermal gradient is at least 3.5 degreesCelsius per 100 meters.

In some embodiments, the geothermal gradient is at least 4.0 degreesCelsius per 100 meters.

In some embodiments, the geothermal gradient is at about 4.5 degreesCelsius per 100 meters.

In some embodiments, the production well is substantially horizontal, acentral axis thereof being substantially parallel to a minimum stressvector of the kerogenous chalk.

In some embodiments, the producing includes drawing naturally-occurringoil residing in pore space of the kerogenous chalk source rock into theproduction well.

In some embodiments, the producing includes drawing naturally-occurringoil residing in the pore space of the kerogenous chalk source rock intothe production well via perforations thereof.

In some embodiments, the method further comprises (i) subjecting theproduced oil to a distillation process and/or (ii) desulfurizing theproduced oil or a derivative thereof and/or (iii) refining the producedoil into at least one of naphtha, gasoline, diesel fuel, asphalt base,heating oil, kerosene, and liquefied petroleum gas.

Some embodiments of the present invention relate to an apparatus for oilproduction comprising: a shallow production well having a maximum depthof at most 2 kilometers drilled into a kerogenous chalk source rock thatis characterized by: i. type IIs kerogen; and ii. a geothermal gradientof at least 4 degrees Celsius per 100 meters wherein at depths that areshallow, above the aquifer and within the source rock, the productionwell is cased and perforated.

In some embodiments, the production well is non-vertical.

In some embodiments, the production well is horizontal.

In some embodiments, the apparatus further comprises a series of thinparallel flow channels each of which leads to the production well and athickness direction of each flow channel being oriented along theproduction well central axis.

In some embodiments, the production well is substantially horizontal, acentral axis thereof being substantially parallel to a minimum stressvector of the kerogenous chalk.

The present invention has been described using detailed descriptions ofembodiments thereof that are provided by way of example and are notintended to limit the scope of the invention. The described embodimentscomprise different features, not all of which are required in allembodiments of the invention. Some embodiments of the present inventionutilize only some of the features or possible combinations of thefeatures. Variations of embodiments of the present invention that aredescribed and embodiments of the present invention comprising differentcombinations of features noted in the described embodiments will occurto persons of the art.

What is claimed:
 1. A method of unconventional oil productioncomprising: a. drilling a production well into a kerogenous chalk sourcerock comprising (i) type IIs kerogen and (ii) shallownaturally-occurring unconventional oil derived from the type IIs kerogenthat is resident within pore space of the source rock; b. at shallowdepths of at most 2 kilometers and within the source rock, casing andperforating the production well; and c. producing the shallownaturally-occurring unconventional oil from the source rock via theproduction well.
 2. The method of claim 1 wherein a location at whichthe production well is drilled is selected in accordance with ageothermal gradient.
 3. The method of any preceding claim wherein theproduction well is drilled at a location where the geothermal gradientis at least 3.0 degrees Celsius per 100 meters, or at least 3.5 degreesCelsius per 100 meters, or at least 4.0 degrees Celsius per 100 meters.4. The method of any preceding claim wherein the unconventional oil andat least some of the perforations of the production well are located atdepths of at most 1.5 kilometers, or at most 1200 meters, or at most 1kilometer or at most 800 meters.
 5. The method of any preceding claimwherein the source rock is below an overburden comprising a basaltlayer.
 6. The method of claim 5 wherein the overburden further comprisesa sedimentary portion situated below the basalt layer so that horizontalstresses of the sedimentary portion were locked in at or before a timeof deposition of the lava flow which formed the basalt layer.
 7. Themethod of any preceding claim wherein a porosity of the source rock isat least 30% or at least 35% or at least 40%.
 8. The method of anypreceding claim wherein a permeability of the source rock matrix is atmost 1 mD or at most 0.1 mD or at most 0.01 mD.
 9. The method of anypreceding claim wherein an oil saturation of pore space of the sourcerock is at least 50% or at least 60% or at least 70%.
 10. The method ofany preceding claim wherein the source rock is stimulated at the shallowdepths to increase a permeability of the source rock.
 11. The method ofclaim 10 wherein the stimulation of the source rock occurs at a depththat is less than that of all aquifers thereof.
 12. The method of any ofclaims 10-11 wherein the source rock is stimulated by means other thanby hydraulic stimulation.
 13. The method of any preceding claim whereina total organic content (TOC) of the source rock is at least 10%. 14.The method of any preceding claim wherein the source rock is stimulatedat the shallow depths by high pressure acid stimulation of the sourcerock.
 15. The method of any preceding claim wherein the source rock ishydraulic stimulated.
 16. The method of any preceding claim wherein thesource rock thermally stimulated.
 17. The method of claim 16 whereinthermal energy is effective to significantly increase the mobility ofthe naturally-occurring oil by at least a factor of
 10. 18. The methodof any of claims 16-17 wherein thermal energy is effective tosignificantly decrease the viscosity of the naturally-occurring oil byat least a factor of
 10. 19. The method of any of claims 16-18 whereinthe thermal energy is effective to vaporize liquid water and lighthydrocarbons within the pore space of the source rock.
 20. The method ofany preceding claim wherein pressurized steam is injected into thesource rock at the shallow depths so as to thermally stimulate thesource rock to increase a mobility of the unconventional oil.
 21. Themethod of claim 20 wherein the steam is injected according to ahuff-and-puff technique.
 22. The method of any of claims 20-21 whereinthe steam enters the source rock at a temperature of at most 200 degreesCelsius.
 23. The method of any preceding claim wherein the productionwell is non-vertical.
 24. The method of claim 23 wherein thenon-vertical production well is substantially horizontally-oriented. 25.The method of any of claims 23-24 wherein the stimulation forms aplurality of parallel, thin flow channels within the source rock thatare each substantially vertically oriented, a thickness direction of theflow channels being along a central axis of the production well, andwith each flow channel leading to the production well.
 26. The method ofany preceding claim wherein the production well is substantiallyhorizontal, a central axis thereof being substantially parallel to aminimum stress vector of the kerogenous chalk source rock.
 27. Themethod of any preceding claim wherein a total organic content (TOC) ofthe source rock is at least 15%.
 28. The method of any preceding claimwherein a sulfur content of the unconventional oil is at least 2.5%wt/wt or at least 3% wt/wt or at least 3.5% wt/wt or at least 4% wt/wt.29. The method of any preceding claim wherein an API gravity of theunconventional oil is at least 20° and/or at most 30°.
 30. The method ofany preceding claim wherein a maximum depth of the production well is atmost 2 km or at most 1.5 kilometers, or at most 1200 meters, or at most1 kilometer or at most 800 meters.
 31. The method of any preceding claimwherein oil produced via the production wells is never heated within thesource rock to a temperature exceeding 200 degrees Celsius
 32. Themethod of any preceding claim, carried out so that bulk source rock isnever heated to a temperature exceeding 200 degrees Celsius.
 33. Themethod of any preceding claim wherein the method is carried out withoutsignificantly pyrolyzing the source rock.
 34. The method of anypreceding claim wherein a majority of hydrocarbon liquids produced viathe production wells is the naturally-occurring oil.
 35. The method ofany previous claim, wherein the producing includes drawingnaturally-occurring oil residing in pore space of the kerogenous chalksource rock into the production well.
 36. The method of any previousclaim, wherein the producing includes drawing naturally occurring oilresiding in the pore space of the kerogenous chalk source rock into theproduction well via perforations thereof.
 37. The method of any previousclaim, further comprising subjecting the produced oil to a distillationprocess.
 38. The method of any previous claim, further comprisingdesulfurizing the produced oil or a derivative thereof.
 39. The methodof any previous claim, further comprising refining the produced oil intoat least one of naphtha, gasoline, diesel fuel, asphalt base, heatingoil, kerosene, and liquefied petroleum gas.
 40. The method of anyprevious claim wherein a geothermal gradient at one or more candidatelocations is analyzed, and the drilling of the production well at itslocation is contingent upon the results of the analysis.
 41. The methodof any previous claim wherein the kerogenous chalk is situated beneath abasalt overburden.
 42. The method of claim 41 wherein a thickness of thebasalt overburden at one or more candidate locations is analyzed, andthe drilling of the production well at its location is contingent uponthe results of the analysis.
 43. The produced oil, or any derivativethereof, produced by the method of any of preceding claim.
 44. Anapparatus for unconventional oil production comprising: a productionwell drilled into a kerogenous chalk source rock comprising (i) type IIskerogen and (ii) shallow naturally-occurring unconventional oil derivedfrom the type IIs kerogen that is resident within pore space of thesource rock, wherein the production well is cased and perforated atshallow depths of at most 2 kilometers and within the source rock sothat the shallow naturally-occurring unconventional oil is recovered bythe production well via the shallow-depth perforations of the productionwell.
 45. The apparatus of claim 44 wherein the production well isnon-vertical.
 46. The apparatus of claim 44 wherein the production wellis horizontal.
 47. The apparatus of any of claims 44-46 furthercomprising a series of thin parallel flow channels that are allvertically oriented and transverse to a central axis of the productionwell.
 48. The apparatus of any of claims 44-47 wherein the productionwell is substantially horizontal, a central axis thereof beingsubstantially parallel to a minimum stress vector of the kerogenouschalk.
 49. The apparatus of any of claims 44-48 wherein at a location ofthe production well, a local geothermal gradient is at least 3.0 degreesCelsius per 100 meters, or at least 3.5 degrees Celsius per 100 meters,or at least 4.0 degrees Celsius per 100 meters.
 50. The apparatus of anyof claims 44-49 wherein the unconventional oil and at least some of theperforations of the production well are located at depths of at most 1.5kilometers, or at most 1200 meters, or at most 1 kilometer or at most800 meters.
 51. The apparatus of any of claims 44-50 wherein the sourcerock is below an overburden comprising a basalt layer.
 52. The apparatusof any of claims 44-51 wherein the overburden further comprises asedimentary portion situated below the basalt layer so that horizontalstresses of the sedimentary portion were locked in at or before a timeof deposition of the lava flow which formed the basalt layer.
 53. Theapparatus of any of claims 44-52 wherein a porosity of the source rockis at least 30% or at least 35% or at least 40%.
 54. The apparatus ofany of claims 44-53 wherein a permeability of the source rock matrix atmost 1 mD or is at most 0.1 mD or at most 0.01 mD.
 55. The apparatus ofany of claims 44-54 wherein an oil saturation of pore space of thesource rock is at least 50% or at least 60% or at least 70%.
 56. Theapparatus of any of claims 44-55 wherein a total organic content (TOC)of the source rock is at least 15%.
 57. The apparatus of any of claims44-56 wherein a sulfur content of the unconventional oil is at least2.5% wt/wt or at least 3% wt/wt or at least 3.5% wt/wt or at least 4%wt/wt.
 58. The apparatus of any of claims 44-57 wherein an API gravityof the unconventional oil is at least 25° and/or at most 30°.